Method for operating an internal combustion engine

ABSTRACT

The operation of an internal combustion engine under unfavorable operating conditions can lead to the formation of deposits in the combustion chamber ( 4 ). A method and an arrangement for operating an internal combustion engine ( 1 ), especially of a motor vehicle, is suggested, wherein fuel is conducted into a combustion chamber ( 4 ) and is there combusted. When deposits are detected in the combustion chamber ( 4 ), measures are initiated in a targeted manner for cleansing the combustion chamber ( 4 ). A knocking combustion is especially introduced and/or a cleansing liquid is added to the inducted combustion air.

FIELD OF THE INVENTION

The invention relates to a method and an arrangement for operating aninternal combustion engine, especially of a motor vehicle, wherein fuelis directed into the combustion chamber and there combusted.

BACKGROUND OF THE INVENTION

The operation of internal combustion engines in the presence ofunfavorable operating conditions can lead to the formation of depositsin the combustion chamber. Especially for engines having direct fuelinjection, deposits can form, for example, on the injection valves, thatis, on the tips or in the tips of the injection valves. These depositscan operate unfavorably on the spray preparation and therefore on thecombustion. As a rule, one speaks of a coking of the injection valves.

An electronic control arrangement is known from DE 198 28 279 A1 bymeans of which an equalization of the cylinder-individual torquecontributions can be carried out in a multi-cylinder engine. Here, tobalance the cylinder-individual torque contributions, the injected fuelquantity, the ignition time point (for a spark-ignition engine), theexhaust gas recirculation rate or the injection position are varied. Thedetermination of the cylinder-individual torque contributions can takeplace via the evaluation of the time-dependent trace of the rotationalmovement of the crankshaft or camshaft and wherein individual segmenttimes are detected. Alternatively, rough running values can be usedwhich are anyway formed in the control apparatus for the detection ofcombustion misfires. The aim of the cylinder equalization is to minimizethe rough running values with a control concept. Correspondinginterventions can be undertaken on the engine in dependence upon thedetected pattern and from the magnitude of the individual filtered andunfiltered rough running values. A coking of injection valves can causea torque of the corresponding cylinder which is too low especially in anengine having direct injection. In this case, the corresponding cylinderruns too lean. The main components for the control function arecylinder-individual PI controllers in correspondence to DE 198 28 279A1.

U.S. patent application publication 2003/0159677 describes a method andan arrangement for monitoring the effects of a cylinder equalizationcontrol. Corresponding to the introduction of the description, it is aspecial requirement for a direct-injecting spark-ignition engine. Here,an increased rough running can occur caused by a low tolerancecompatibility of the combustion process in stratified operation and/orbecause of tolerances of the high pressure injection valves which areused or in the distribution of the fuel to the individual cylinders.Also, deterioration-caused changes of the throughflow characteristics ofthe high pressure injection valves can have an effect. In the context ofU.S. patent application publication 2003/0159677, preferably the torquecontribution (actual torque) of a cylinder relative to its ignitionpredecessor is detected (that is, no absolute torque determination) viaan evaluation of the time-dependent trace of the crankshaft rotation orcamshaft rotation. Improvements in the area of cylinder equalization areachieved in that a monitoring of the effects for the cylinderequalization control is provided and in that a corresponding faultsignal is generated for disturbances in the area of the cylinderequalization control. The monitoring of the effects takes place in sucha manner that the cylinder-individual torque contributions can bechecked after a completed cylinder equalization control intervention todetermine if the control shows an effect. If the effect does not occurto the extent as wanted, the control loop amplification of thecylinder-individual PI controllers is successively reduced to a pregivenend value. The control thereby functions with greater robustness but isdynamically slower which is accepted. If the wanted effect does notoccur after adjusting the PI controllers to the pregiven end value, thena fault signal is generated.

The disclosure of the last-mentioned U.S. patent application publication2003/0159677 is expressly incorporated into this application.

SUMMARY OF THE INVENTION

The present invention has as its object to provide a method of the abovekind with which depositions in the combustion chambers of the engine canbe detected and removed in a simple manner.

The especially great advantage of the present invention is that thecombustion chamber can be kept free of deposits with simple means overthe entire service life of the engine, whereby always optimal conditionsare given for a good combustion.

A further advantage of the invention is that the combustion temperatureis reduced with the injection of water and, associated therewith, theNOx emission becomes lower. Furthermore, the thermodynamic efficiency ofthe engine is improved because of the water vapor pressure of the watervaporized in the combustion chamber at high temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with respect to the drawings.

FIG. 1 schematically shows an internal combustion engine having acontrol apparatus;

FIG. 2 shows a flowchart of the method of the invention; and,

FIG. 3 schematically shows an internal combustion engine having acontrol apparatus and having a device with which water or any otherdesired cleaning liquid can be added to the inducted combustion air.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1, an internal combustion engine 1 is shown wherein a piston 2 ismovable back and forth in a cylinder 3. The cylinder 3 is provided witha combustion chamber 4 to which an intake manifold 6 and an exhaust-gaspipe 7 are connected via valves 5. Furthermore, an injection valve 8 anda spark plug 9 are associated with the combustion chamber 4. Theinjection valve 8 is driven by a signal TI and the spark plug 9 isdriven by a signal ZW. The signals TI and ZW are transmitted by acontrol apparatus 16 to the injection valve 8 and the spark plug 9,respectively.

The intake manifold 6 is provided with an air mass sensor 10 and theexhaust-gas pipe 7 is provided with a lambda sensor 11. The air masssensor 10 measures the air mass of the fresh air supplied to the intakemanifold 6 and generates a signal LM in dependence thereon. The lambdasensor 11 measures the oxygen content of the exhaust gas in theexhaust-gas pipe 7 and generates a signal lambda in dependence thereon.The signals of the air mass sensor 10 and of the lambda sensor 11 aresupplied to the control apparatus 16.

A throttle flap 12 is accommodated in the intake manifold 6 and therotational position of the throttle flap is adjusted by means of asignal DK.

In a first mode of operation, the stratified operation of the engine 1,the throttle flap 12 is opened wide. The fuel is injected into thecombustion chamber 4 by the injection valve 8 during a compression phasecaused by the piston 2. Then, the fuel is ignited with the aid of thespark plug 9 so that the piston 2 is driven in the next work phase bythe expansion of the ignited fuel.

In a second operating mode, the homogeneous operation of the engine 1,the throttle flap 12 is partially opened or closed in dependence uponthe desired supplied air mass. The fuel is injected into the combustionchamber 4 by the injection valve 8 during an induction phase caused bythe piston 2. Because of the simultaneously inducted air, the injectedfuel is swirled and it is thereby essentially uniformly distributed inthe combustion chamber 4. Thereafter, the air/fuel mixture is compressedduring the compression phase in order to then be ignited by the sparkplug 9. The piston 2 is driven with the expansion of the ignited fuel.

In the stratified operation as well as in the homogeneous operation, arotational movement is imparted by the driven piston to a crankshaft 14via which the wheels of the motor vehicle are driven. A toothed wheel 16is mounted on the crankshaft 14 and the teeth thereof are scanned by anrpm sensor 15 mounted directly opposite. The rpm sensor 15 generates asignal from which the rpm N of the crankshaft 14 is determined and thesensor transmits this signal to the control apparatus 16.

The fuel mass, which is injected into the combustion chamber by theinjection valve 8 in stratified operation and in homogeneous operation,is controlled (open loop and/or closed loop) by the control apparatus 16especially with the view to a low consumption of fuel and/or a lowdevelopment of toxic substances. For this purpose, the control apparatus16 is provided with a microprocessor which has a program stored in astorage medium, especially in a read-only-memory (ROM), which program issuited to carry out the entire control (open loop and/or closed loop) ofthe engine 1.

Input signals are applied to the control apparatus 16 and representoperating variables of the engine which are measured by means ofsensors. For example, the control apparatus 16 is connected to the airmass sensor 10, the lambda sensor 11 and the rpm sensor 15. Furthermore,the control apparatus 16 is connected to an accelerator pedal sensor 17which generates a signal FP, which indicates the position of anaccelerator pedal actuated by the driver and therefore the torquecommanded by the driver. The control apparatus 16 generates outputsignals with which the performance of the engine 1 can be influenced incorrespondence to the desired control (open loop and/or closed loop) viaactuators. For example, the control apparatus 16 is connected to theinjection valve 8, the spark plug 9 and the throttle flap 12 andgenerates the signals TI, ZW and DK, which are needed to drive theforegoing.

FIG. 2 shows a flowchart of the method of the invention especially foran internal combustion engine having gasoline-direct injection.

Step 215 is described in FIG. 2. In this step, an inquiry is made as tothe effect of the cylinder equalization control and is based, forexample, on the method for monitoring the effects of a cylinderequalization control described in U.S. patent application publication2003/0159677. The input data needed herefor are supplied by the rpmsensor 15 to the control apparatus 16, which, on this basis, undertakesthe control/adaptation of the cylinder-individual torque contributions.For this purpose, for example, the injected fuel quantity TI, theignition time point ZW, the exhaust-gas recirculation rate (not shown inFIG. 2) or the injection position DK is varied by the control apparatus16.

After a start of the method, a check is made in step 210 as to whetherstratified operation is present. As long as no stratified operation isgiven, this inquiry is carried out continuously. If, in contrast,stratified operation is present, then a check is made in step 215 as towhether a fault signal of the monitoring of effects is present. If thisis the case (that is, the cylinder equalization shows no effect), atransition is made directly to step 250, which is described in detailhereinafter. Accordingly, a conclusion is directly drawn as to coking.If, in contrast, it is established in step 215 that the monitoring ofthe effects of the cylinder equalization generates no fault signal, thena check is made in step 220 as to whether combustion misfires occur inthe operating mode “stratified operation”. If no combustion misfires canbe determined, then there is a return to step 210. If, in contrast,combustion misfires are detected, then, there is a switchover in step230 from the operating mode “stratified operation” into the operatingmode “homogeneous operation” with the aid of the control apparatus 16.

In step 240, as already in step 220, a check is made in the operatingmode “homogeneous operation” as to whether combustion misfires occur. Ifno combustion misfires are determined, then a conclusion is drawntherefrom in step 250 that the injection valves are coked, that is,deposits have formed on the injection valves.

Deposits on the injection valves can lead to the spray preparation beingdisturbed in the direct injection of gasoline. Approximately the samefuel quantity is injected into the combustion chamber 4 but the sprayform or the spray guidance is changed because of the deposits. This hasnegative effects especially in stratified operation because, at theignition time point, no ignitable air/fuel cloud is present in thedirect vicinity of the spark plug 9 whereby combustion misfires occur oreven no combustion takes place. In the homogeneous operation, a slightcoking of the injection valves disturbs little because here thecombustion is not essentially dependent upon the spray guidance of theinjected fuel. The fuel is injected early, namely, already during theinduction phase, whereby sufficient time is present for a uniformdistribution.

In step 260, measures are initiated in order to remove the deposits onthe injection valves 8. Alternatively to ending the method shown in FIG.2, a jump back to step 210 can take place after step 260 in order tocheck whether the measures for combustion chamber cleaning weresuccessful. This alternative is indicated by a broken line.

A knocking combustion can be used as a measure for removing deposits.Investigations on internal combustion engines, which were operated withknocking combustion, show that these engines have very clean combustionchambers. This effect is utilized in this invention.

This can be attributed to pressure fluctuations which are generated bythe knocking combustion, with these pressure fluctuations beingsuperposed on the normal pressure trace. With the additional pressurefluctuations, intense high frequency vibrations are generated wherebythe deposits in the combustion chamber 4 and especially on the nozzlesof the injection valves 8 can be removed. The knocking combustion mustbe limited in time in order to avoid damage to the engine 1.

Also, water or any desired other cleaning liquid can be added to theinducted combustion air in combination with the knocking combustion oreven as an independent method whereby a similar cleaning effect can beachieved as with the knocking combustion. Investigations of engineswherein water has penetrated into the combustion chamber 4 (via anon-tight cylinder head seal or injected additionally) have shown thatthese engines always have especially clean combustion chambers.

This effect is used in this invention.

After the combustion cleaning has been carried out, a switchover tostratified operation again takes place in order to check whether theengine 1 runs without misfires. If misfires are again determined, themethod can again be started anew.

As a precaution or to avoid the occurrence of deposits in the combustionchamber, a knocking combustion can be carried out and/or water can beadded to the air at specific time intervals.

If combustion misfires were detected in step 240 also in homogeneousoperation, then, in step 270, a further diagnostic method is started.The combustion misfires, in this case, cannot be caused exclusively bydeposits on the nozzles of the injection valves. For example, thesecombustion misfires can also be cause by an injection valve 8, which nolonger opens in a controlled manner, or by a defective spark plug 9. Acoking of the injection valves 8 can, in this case, not be completelyprecluded. In any case, the reasons for these combustion misfires mustbe narrowed by further diagnostic methods. A corresponding storage ofthe faults in a fault memory can be helpful in a later repair in orderto obtain a precise diagnosis.

FIG. 3 shows an internal combustion engine 1 having a control apparatus16, as already shown in FIG. 1, and with a device with which water orany desired other cleaning liquid can be added to the air. For the sakeof simplicity, the reference numerals of FIG. 1 are taken over for thesame components.

A water vessel 18 is additionally mounted on the engine 1. A valve 19 ismounted on the water vessel 18 which can be driven with the aid of thecontrol apparatus 16. The valve 19 is connected to an injection nozzle20. With the aid of the nozzle 20, water can reach directly into theintake manifold 6 when actuating the valve 19.

If, for example, deposits on the injection valves 8 are detected by thecontrol apparatus 16, a signal WA is generated with which the valve 19is driven or opened. Because of the underpressure which, as a rule, ispresent in the intake manifold 6, water is introduced into the intakemanifold 6 from the water vessel 18 via the valve 19 and the nozzle 20when the valve 19 is opened. With the next induction operation of theengine 1, water in the intake manifold 6 reaches the combustion chamber4. There, the water mixes with the air and fuel reaching the combustionchamber during the injection operation. Because of the high temperaturein the combustion chamber 4, the water vaporizes immediately andcontributes to the cleaning of the combustion chamber.

Although an internal combustion engine having gasoline direct injectionwas selected as an example, it is possible to apply this method in asomewhat modified form even to other internal combustion engines such asa diesel engine or an internal combustion engine having intake manifoldinjection.

A special embodiment of the method of the invention is its realizationin the form of a computer program having program code means. Such acomputer program can be stored on a storage medium such as a CD-ROM oran EPROM and makes it possible to introduce the method steps of theinvention for combustion chamber cleanup when the computer program isexecuted in a control apparatus (that is, generally in any desiredcomputer). In this way, it affords the manufacturer of such a product asimple possibility to supply the product to a customer.

1. A method for operating an internal combustion engine including anengine for a motor vehicle, the method comprising the steps of:directing fuel into a combustion chamber of said engine and combustingsaid fuel therein; drawing a conclusion as to deposits in saidcombustion chamber from at least monitoring the effects of a cylinderequalization during operation of said engine; and, thereafter initiatingmeasures in a targeted manner for cleansing said combustion chamberwhile said engine continues to be in operation.
 2. The method of claim1, comprising at least one of the following further steps of: bringingabout a knocking combustion to cleanse said combustion chamber; and,adding a cleansing or detergent liquid to combustion air inducted bysaid engine.
 3. The method of claim 2, wherein said cleansing liquid iswater.
 4. The method of claim 2, wherein said measures are conducted fora predetermined time duration.
 5. The method of claim 2, wherein saidmeasures for cleansing said combustion chamber are carried out so longuntil no deposits are detected in said combustion chamber.
 6. The methodof claim 5, wherein said measures for cleansing said combustion chamberare carried out only so long as no damage to said engine is to beexpected.
 7. The method of claim 1, wherein said measures for cleansingsaid combustion chamber are carried out as a precaution at predeterminedtime intervals for a predetermined time duration.
 8. A method foroperating an internal combustion engine including an engine for a mothervehicle, the method comprising the steps of: directing fuel into acombustion chamber of said engine and combusting said fuel therein;drawing a conclusion as to deposits in said combustion chamber from atleast monitoring the effects of a cylinder equalization; thereafterinitiating measures in a targeted manner for cleansing said combustionchamber; directly injecting fuel into the combustion chambers of saidengine with the aid of injection valves in a first operating mode duringa compression phase or in a second operating mode during an inductionphase; continuously carrying out a misfire detection; when detectingmisfires during operation of said engine in said first operating mode,then switching over into the second operating mode; and, when misfiresalso occur in the second operating mode, drawing a conclusion as to ageneral fault and starting additional diagnostic methods for narrowingdown the fault causes.
 9. The method of claim 1, wherein said engine isa diesel engine.
 10. A method for operating a direct-injecting internalcombustion engine including an internal combustion engine of a motorvehicle, the method comprising the steps of: directly injecting fuelinto the combustion chambers of said engine with the aid of injectionvalves in a first operating mode during a compression phase or in asecond operating mode during an induction phase; continuously carryingout at least one of a cylinder equalization with monitoring of effectsand a misfire detection; drawing a conclusion as to the coking of theinjection valves when a fault signal of said monitoring of effects ispresent or, when detecting a misfire during operation of said engine insaid first operating mode, switching over to said second operating mode;and, when no misfire occurs in said second operating mode, drawing aconclusion as to deposits on the nozzles of said injection valves or acoking of said injection valves.
 11. The method of claim 10, comprisingat least one of the following further steps of: bringing about aknocking combustion to cleanse said combustion chamber; and, adding acleansing or detergent liquid to combustion air inducted by said engine.12. The method of claim 11, wherein said cleansing liquid is water. 13.The method of claim 11, wherein said measures are conducted for apredetermined time duration.
 14. The method of claim 11, wherein saidmeasures for cleansing said combustion chamber are carried out so longuntil no deposits are detected in said combustion chamber.
 15. Themethod of claim 14, wherein said measures for cleansing said combustionchamber are carried out only so long as no damage to said engine is tobe expected.
 16. The method of claim 10, wherein said measures forcleansing said combustion chamber are carried out as a precaution atpredetermined time intervals for a predetermined time duration.
 17. Acomputer program comprising: program-code means for carrying out amethod for operating an internal combustion engine when executed on acomputer, the method including the steps of: directing fuel into acombustion chamber of said engine and combusting said fuel therein;drawing a conclusion as to deposits in said combustion chamber from atleast monitoring the effects of a cylinder equalization during operationof said engine; and, thereafter initiating measures in a targeted mannerfor cleansing said combustion chamber while said engine continues to bein operation.
 18. A control apparatus for operating an internalcombustion engine including an internal combustion engine of a motorvehicle, the control apparatus comprising: means for controlling thesupply of fuel into a combustion chamber of said engine and combustingsaid fuel therein; means for drawing a conclusion as to deposits in saidcombustion chamber from at least monitoring the effects of a cylinderequalization during operation of said engine; and, means for initiatingmeasures in a targeted manner for cleansing said combustion chamberwhile said engine continues to be in operation.
 19. An internalcombustion engine including an engine for a motor vehicle, the internalcombustion engine comprising: a cylinder and a piston conjointlydefining a combustion chamber; means for metering fuel to saidcombustion chamber; and, a control apparatus functioning to: control themetering of fuel into a combustion chamber of said engine and combustingsaid fuel therein; draw a conclusion as to deposits in said combustionchamber from at least monitoring the effects of a cylinder equalizationduring operation of said engine; and, thereafter initiate measures in atargeted manner for cleansing said combustion chamber while said enginecontinues to be in operation.